Watching Lungs Work Through a Crystal Ribcage

Hadi Nia, Ph.D. wanted to learn about the inner workings of the lung in a way nobody had, but he knew he’d need something close to a crystal ball to see what was really happening. 

That idea, it turns out, wasn’t exactly far-fetched. Nia, an assistant professor in the Biomedical Engineering department at Boston University, already knew a thing or two about diving deep into the fundamentals of how organs work. He’d spent his postdoctoral training at Massachusetts General Hospital learning intravital microscopy, a technique that uses transparent windows implanted into different organs of live lab animals – for example, their brains or livers – to document what was happening inside.

“But I noticed there was no good model for the lung,” said Nia. “In the existing models, once you implant the window into the lung, it immobilizes it and all respiratory function is gone.”

So when he started his own lab at BU, he and his team designed something decidedly better: technology for studying the lung ex vivo – or outside of the body – while it is still breathing and supplied with a blood supply. The technology relies on a never-before-seen protective shield called the crystal ribcage, a clear structure that has similar properties of the lab mouse ribcage and allows researchers to image the lung in real time. It’s no small feat, given that the lung is an organ continuously in motion. In fact, Nia’s idea was so novel and potentially transformative, he received a nearly $1.5 million NIH Director’s New Innovator Awards in 2022, administered by NHLBI, to develop it further. 

Visualizing a vital organ

The lung may be one of our most critical organs, but it’s plenty vulnerable. Not only does it face a slew of daily threats from airborne pathogens and pollutants; it’s also the site of many fatal diseases, like primary and metastatic cancers, respiratory infections, and obstructive and restrictive diseases like COPD and pulmonary fibrosis. While procedures such as MRI and CT scans can shed critical light on what’s going wrong when a patient has lung disease or illness, these techniques fail to provide the real-time information key to fully understanding the intricate workings of the lung at the cellular resolution.

Crystal ribcage does just that. It allows researchers to witness the moment-to-moment dynamics of respiration and circulation, the body’s response to airborne pathogens, and what happens when tumor and immune cells move into the lungs. Nia’s system uses a ventilator and perfusion pump to keep the lung functioning outside the body while maintaining its natural shape. The crystal ribcage that encloses it then makes optical imaging of the organ possible, and researchers can capture everything from the entire lung to a single lung cell.  

“You can study cancer, pneumonia, or almost any pulmonary diseases that affect the surface of the lung,” said Nia.

Using a 3D printed model, his team designed the crystal ribcage to perfectly replicate the geometry and properties of the mouse ribcage. The inside is slippery like a real ribcage to allow the lungs to easily slide back and forth during normal breathing. Nia’s team went one step further, though: to capture other breathing patterns, they designed two versions of the crystal ribcage using different types of bio-compatible plastics – one rigid and one semi-rigid.

“The rigid version closely mimics the ribcage in normal breathing,” said Nia. “When we use quiet breathing, about 95% of the movement comes from the diaphragm and only 5% comes from rib motion.” In contrast, the semi-rigid ribcage imitates the large movement of the ribcage that happens during exercise, sighing, and coughing. 

Crystalizing the technology

“One of the most unique applications of the crystal ribcage is studying disease progression,” said Nia. “Not only can you study how a disease starts to develop, but you can also investigate how it responds to therapies.” This provides enormous opportunities for homing in on the cause and effect of diseases. 

One lung disease that the Nia lab focuses on is pneumonia. The researchers have found that the immune cell migration to the lung that happens after infection is responsive to blood pressure changes. When the blood pressure increases, the immune cells flock to the site of infection faster, and when it decreases, the immune cells act less swiftly. This suggests that when capillaries and the blood pressure inside them are altered by a disease such as pneumonia, the activity of immune cells are altered in those regions, too, and this may affect the progression of the disease. 

“While we don't know the mechanism for how this happens, we do know that this doesn’t happen in cells in petri dishes,” said Nia. “It’s a good example of how to study many of these disease events in the actual organ instead of an overly simplified model in a dish.”

His team also uses the crystal ribcage to study cancer metastasis, as the movement of cancer cells throughout other parts of the body is the cause of most cancer deaths, not the cancer that showed up first. The question for Nia’s team is why some metastasized cancer cells form a tumor, and some don’t. Using the new technology, researchers can now track a single cancer cell in real time as it travels throughout the lung tissue, pinpointing which characteristics of that cell cause it to form a tumor rather than be eliminated by the immune cells.

Even though this technology is currently used for mouse lungs, Nia and his team are looking at developing the crystal ribcage for larger animals, such as pig and transplant-rejected human lungs, to probe diseases and therapeutics in a more clinically relevant setting.

And they have loads of other ideas for how to apply this technology. As strange as it sounds, these include imaging air. “No one has imaged the air inside the alveoli, the tiny air sacs in the lung that exchange oxygen and carbon dioxide,” said Nia, “yet we can see how a single droplet arrives and deposits on the surface of an alveolus, just as pathogens such as SARS-CoV-2 can infect the alveoli,” he said. These images, in turn, can be used for early infectious disease models that researchers develop when studying airborne illnesses.

Further, imaging air could be used to better understand medications that are inhalation-based. “Being able to image the airborne particles, we can see exactly what cells will receive the drug and what cells don’t.”

For Nia, the possibilities for crystal ribcage seem endless, and the pace of insights he and his team are gaining, exhilarating. “Never in a million years would I have thought that we could see the entire surface of a functioning lung in real-time at the cellular level,” he said. “But here we are. Using the crystal ribcage for life-saving discoveries is no longer unthinkable, and I’m thrilled.”